THE MOTION OF WATER MASERS IN THE PRE-PLANETARY NEBULA IRAS 16342-3814

We present high angular resolution observations, using the Very Long Baseline Array of the NRAO(4), of the high-velocity water masers toward the "water fountain" pre-planetary nebula, IRAS 16342-3814. The detailed structure of the water masers appears to be that of bow shocks on either side of a highly collimated jet. The proper motions of the water masers are approximately equal to the radial velocities; the three-dimensional velocities are approximately +/- 180 km s(-1), which leads to a very short dynamical timescale of similar to 100 yrs. Although we do not find direct evidence for precession of the fast collimated jet, there may be indirect evidence for such precession.